Conventional prior art portable lathes employed for machining the abutting ends of pipe for welding are constructed to be secured to the pipe by a central support mandrel engaging the internal surface of the pipe. During the machining operation, the lathe cutting tool is rotated and axially fed to machine the pipe end while the lathe is coupled to the pipe via the central support mandrel. Such prior art lathes produce acceptable results when machining medium and large diameter pipe. However, when machining smaller diameter pipe, the reduced strength of the smaller diameter mandrel, primarily its reduced stiffness to bending, results in erratic machining and tool chatter. Economics demands that a given portable lathe be useful for a range of pipe sizes; however, with prior art portable lathe designs, the stiffness requirement at the small end of the pipe size range cannot be met without substantially increasing the lathe weight and therefore without adversely affecting its portability.